Pd-catalyzed aerobic oxidative coupling of arenes provides efficient access to biaryl compounds. The biaryl product forms via C-H activation of two arenes to afford a (PdArAr)-Ar-II' intermediate, which then undergoes C-C reductive elimination. The key (PcArAr)-Ar-II' intermediate could form via a "monometallic" pathway involving sequential C-H activation at a single Pd-II center, or via a "bimetallic" pathway involving parallel C-H activation at separate Pd-II centers, followed by a transmetalation step between two Pd-II-aryl intermediates. Here, we investigate the oxidative coupling of o-xylene catalyzed by a PdX2/2-fluoropyridine catalyst (X = trifluoroacetate, acetate). Kinetic studies, H/D exchange experiments, and kinetic isotope effects provide clear support for a bimetallic/transmetalation mechanism.